The invention relates to a method of manufacturing an electrically conductive pattern of tin-doped indium oxide (ITO) on a substrate, in which method a layer of tin-doped indium oxide is provided on the substrate after which the layer is structured lithographically using an aqueous etching bath which contains halogen acid.
The invention also relates to a method of manufacturing a supporting plate for a liquid crystal display device, which supporting plate has patterns of tin-doped indium oxide as well as conductors of a metal which dissolve in an oxidizing etching bath, in particular a metal selected from the group consisting of Mo, W and TiW.
The invention further relates to the use of an etching bath consisting of an aqueous solution of halogen acid and a liquid selected from the group consisting of acetic acid and methanol for selectively etching ITO relative to metals which dissolve in an oxidizing etching bath, in particular a metal selected from the group consisting of Mo, W and TiW,
Such a method is used, for example, in the manufacture of electrooptical display devices such as liquid crystal display devices (LCDs), electroluminescent display devices, photocells and solid-state image sensors, In an LCD, a liquid crystalline medium is sandwiched between two parallel glass supporting plates. Transparent electrodes which generally consist of semiconductive metal oxide such as tin-doped indium oxide, are provided on the sides of the supporting plates facing the medium. The latter material is commonly referred to as ITO and can be provided on the supporting plates in the form of a layer by sputtering, vacuum deposition, Chemical Vapour Deposition (CVD) or by hydrolysis and pyrolysis of a corresponding metal compound, The ITO layer generally has a thickness in the range between 20 and 400 nm and comprises, for example, 2-10 atom % of tin, The desired electrode pattern is obtained by etching the ITO layer, in accordance with a pattern, using a suitable chemical etchant,
U.S. Pat. No. 4,093,504 discloses a method of manufacturing patterns of ITO, in which method a photoresist layer is provided on an ITO layer, after which the photoresist layer is exposed to patterned radiation and then developed. ITO is subsequently etched using an etching bath consisting of a mixture of hydrochloric acid and FeCl.sub.3, thereby forming the ITO pattern. The presence of FeCl.sub.3 increases the etching rate of the ITO.
A disadvantage of the known method is that FeCl.sub.3 is harmful to the environment. Another disadvantage is the oxidizing property of FeCl.sub.3, which causes not only ITO but also some other metals present on certain types of LCD panels, for example Mo, to be attacked. Thus, the known etching bath is not a selective ITO etchant.